PID Controller:

Pseudo-Code Within the Controller Class:

  • error = sensorValue – offset(target)
  • integral = integral * dampen + error
  • derivative = error – lastError
  • pTerm = Kp*error
  • iTerm = Ki*integral
  • dTerm = Kd*derivative
  • correction = pTerm + iTerm + dTerm

Pseudo-Code in the Control Task:

  • correction = Range.clip(correction, original min, original max)
  • correction = Range.clip(correction, original min, original max, scaled min, scaled max)
  • power = Range.clip(tp ± correction, -1, 1) – ALWAYS clip to (-1, 1) when setting motor power

PID Controller Class

  • Instantiate a controller for each control task (line following, turning, go forward etc.)
  • Instantiate with parameters(Controller name, Kp, Ki, Kd, dampen)
  • Can control debugging by setting debug mode on or off with .setDebug() method
    • writes the error, lastError, integral, derivative, pTerm, iTerm, dTerm, correction with the timestamp
    • writes to the file /FIRST/{controller-name}.txt, one row per iteration
    • ONLY use when debugging (costly/consuming when doing file IO(input output) for every iteration)
    • clear the file BEFORE each run (prevents it from appending to the same file on different runs)
  • Has writeToDebugFile() method to write all messages to file at the end of the control task
    • writes to the file /FIRST/debugFor{controller-name}_{time-stamp}.txt, one row per iteration

Tuning the PID Controller – A 2-step Process!

  • Step 1: Finding the right scale (P controller only)
    • Instantiate controller with Ki, Kd and dampen all set to zero
    • Adjust Range.scale(correction, original min, original max, scaled min, scaled max) until you find the scaled min/max which efficiently completes the task
  • Step 2: Finding the balance between Kp, Ki, Kd
    • Ki starting value (1/10th of Kp)
    • Kd starting value (10 times Kp)
    • Dampen starting value (0.66)

Tuning the Line Follower:

Kp = 1.07, Ki = 0, Kd = 0, dampen = 0 (tp = .2, scale = [-.5, .5])

Observations:

  • Follows the line with significant oscillation
  • Relatively fast

Kp = 1, Ki = 0.1, Kd = 0, dampen = 0.15 (tp = .2, scale = [-.7, .7])

Observations

  • Follows the line with significant oscillation
  • Overshoots after oscillating once
  • Staggered movement

Kp= 1, Ki = 0.1, Kd = 10, dampen = 0.15 (tp = .2, scale = [-.5, .5])

Observations

  • Follows the line with even more significant oscillation
  • Relatively fast

Kp = 1, Ki = .098, Kd = 10, dampen = 0.15(tp = .2, scale = [-.5, .5])

  • Follows line with little oscillation
  • Relatively fast


          


4/16/16 Software
			

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